One question to ask about the author of a book about marriage, as well as the reviewer of a book on marriage and the endorser(s) of a book in marriage, is, “How long has this person been happily married to the same spouse?”
For example, why would anyone listen to Oprah Winfrey’s opinion on marriage?
Exactly. I paid much more attention to my Grandparents. They'd been married 61 years, before Grandpa passed away a couple of years back.
Of course, I rarely (if ever) have paid attention to *anything* Orpah has pontificated on. So, I suppose Grandma and Grandpa win by default, anyway.